1. Field of the Invention
The present invention relates generally to satellite based positioning systems such as GPS and more specifically to the measurement and monitoring of the signals transmitted by differential satellite augmentation systems.
2. Description of Related Art
A satellite based positioning system is used to determine a position of a receiver and typically includes a plurality of satellites, the receiver, and one or more ground stations. Each of the satellites transmits a signal that contains a code and certain prescribed information useful to the receiver in determining its position.
The receiver synchronizes itself to the codes of at least four satellites and uses the information in the signals from these satellites in order to perform a triangulation-like procedure so as to determine its coordinates with respect to a reference, such as the center of the Earth and the GPS standard time. The receiver is not constrained to a specific location and, therefore, represents a variable position. The purpose of the satellite based positioning system is to make it possible for the receiver to determine its position regardless of the location of the receiver.
The accuracy of the position determined by the receiver is adversely affected by conditions that are common to all receivers in a given area. A ground station containing a receiver in a fixed location is used to monitor the signals transmitted by the satellites and determines corrections to the transmitted satellite signal. The ground station notifies the receiver of any necessary signal corrections to allow the receiver to make more accurate position calculations. This arrangement is referred to as differential positioning.
Since the mobile receiver completely relies on the corrections transmitted from the ground station as being correct, any condition that is inconsistent between the satellite measurements made at the mobile receiver and the ground station will cause a an undetected error in the mobile receiver. To protect the mobile receiver, the ground station monitors the signals transmitted by the satellites in order to detect faults within the satellites that would affect the mobile receiver. This function of detecting faults is referred to as providing integrity for the corrections that the ground station sends to the mobile receiver. For GPS, these faults include signal power, code signal deformation, code and carrier divergence, radio frequency interference, signal acceleration and erroneous ephemeris data.
The ground station system is also referred to as an augmentation system, since it augments both the accuracy and integrity of the original navigation satellite signals. There are two classes of augmentation systems: (1) Satellite Based Augmentation System (SBAS) that provides differential positioning across a wide area like the continental US, and (2) Ground Based Augmentation System (GBAS) that provides differential positioning to a smaller area, up to about 200 miles.
The known SBAS architecture used for wide-area coverage is shown in FIGS. 1 and 2. In the SBAS architecture 10, a network of receivers 14 is used to collect satellite data 120, and perform measurements 110, from the navigational satellites 20 over a satellite to receiver communication path 214 and determine augmentation data 132, which includes differential corrections, ionospheric delay errors, and accuracy of the navigation satellite signals at the receivers"" 14 location.
This measurement data 110 is transferred from the receiver 14 to one or more master stations 12 via a receiver to master station communication path 232. The master stations 12 are centralized data processing sites used to determine differential corrections and integrity of the augmentation 110 over the SBAS Area of Coverage 16. The processed SBAS correction and integrity data 132 is then sent to an SBAS satellite 18 via a master station to satellite communication path 212. This SBAS satellite 18, that generally functions as a communications repeater, then broadcasts the correction and integrity data 132 via a satellite to SBAS user communication path 218 to any user 23 within the area of coverage 16. This structure is illustrated in more detail in FIG. 2.
According to FIG. 3, the Ground Based Augmentation System (GBAS) 30 contains GBAS receivers 32 that measure navigation satellite data 120 provided by the satellite 20 via a satellite to GBAS receiver communication path 240. These receivers 32 communicate satellite data and ranging measurements 150 to a GBAS processor 34 that determines the differential corrections and integrity of the satellite signals. The processor 34 communicates these corrections and integrity data 152 through a local area transmitter 36 to a GBAS user receiver 38 within the GBAS coverage area. Typically the area of coverage for a GBAS is 30 to 50 miles. This smaller coverage volume allows the GBAS to provide greater levels of accuracy and integrity than the SBAS.
The greater levels of accuracy and integrity lend the GBAS to precision airplane approach applications. Due to the strict integrity requirements of precision approach applications, current GBASs, such as those defined by the FAA in FAA Specification FAA-E-2937A (xe2x80x9cFAA-E-2937Axe2x80x9d), herein incorporated by reference, contain monitors for detecting the integrity of the satellite signal waveform as well as the integrity of the ranging measurement from the satellites. Use of these monitors and other requirements allow the accuracy, continuity and integrity of GBAS to be much greater than that of SBAS.
Allowing for more complex operations like precision approach in the SBAS coverage volume requires a greater level of integrity and monitoring than is provided by current SBAS implementations. Two known solutions for addressing enhanced integrity on SBAS have been previously considered.
The first solution applies additional SBAS reference receivers 14 to provide additional sampling points within the coverage area 16. The measurements from these additional receivers 14 develop a more detailed differential and ionospheric correction. Unfortunately, additional receivers 14 add cost for the receivers 14 and communication links 232, 234.
The second solution includes, in the SBAS receivers 14, satellite signal monitors similar to that required per FAA-E-2937A. These monitors would increase the integrity of the measurements made by the receivers by monitoring for the types of anomalies defined in FAA-E-2937A. However, this solution also requires additional costs to update the numerous current receivers 14 that exist with these new monitors.
The present invention utilizes the resources of the GBAS station to supplement the measurement and integrity requirements of the of the SBAS station receivers. This is accomplished by an inventive rigorous communication link between the GBAS stations and the SBAS master station and the necessary processing, translation and storage of related information. The present invention also improves the functionality of the GBAS stations by exchanging data between the various GBAS stations on the communication link.
In its most rudimentary form, the GBAS passes raw measurements, corrections, integrity measurements, and integrity monitoring results to the SBAS station via this rigorous link. The SBAS station can utilize this data to produce corrections and monitoring consistent with the same level of rigor as the GBAS system and thereby increasing the SBAS stations integrity. This communication function and master station function mitigate the hazardous and misleading effects that can be caused on the SBAS user by the SBAS receiver. Thus the SBAS receiver can be can be developed to a lower level of certification or potentially completely removed.
Individual GBAS stations can use the data collected from other GBAS stations on the communication link to improve the functionality and integrity of the corrections produced over those produced by the GBAS system alone. The functionality is increased since the GBAS network can produce wide area corrections similar to the known SBAS implementation and could as such replace the SBAS receivers with a GBAS system that would also provide local area service. The integrity of the GBAS system can improved with the GBAS network data by using measurements from other GBAS systems to monitor effects of satellite signals that vary only over long distances such as ionospheric effects. These effects are challenging for GBAS to monitor since the effect is difficult to isolate with measurements made over the short distances between the GBAS receivers. Using measurements from other GBAS stations a greater distance away makes these determinations simpler to perform with greater integrity.
Specifically, the invention relates to a ground based augmentation system (GBAS) network, comprising: a navigation satellite; an interconnecting system communication network; at least a first GBAS and a second GBAS, each GBAS comprising: a GBAS receiver that is configured to receive navigation satellite data from the navigation satellite and covert it into GBAS raw augmentation data; a GBAS processor that is configured to receive GBAS raw augmentation data from the GBAS receiver and to format it into formatted GBAS differential correction and integrity data; and a GBAS transmitter configured to send GBAS differential correction and integrity data to the interconnecting system communication network; the GBAS processor of the first GBAS being configured to receive GBAS differential correction and integrity data produced by the second GBAS and to include this data in its own formatted GBAS differential correction and integrity data.
The invention also relates to an integrated satellite based augmentation system (SBAS)-GBAS comprising: a navigation satellite; an interconnecting system communication network; one or more GBASs, each GBAS comprising: a GBAS receiver that is configured to receive navigation satellite data from the navigation satellite and covert it into GBAS raw augmentation data; a GBAS processor that is configured to receive GBAS raw augmentation data from the receiver and to format it into formatted GBAS differential correction and integrity data; and a GBAS transmitter configured to send GBAS differential correction and integrity data to the interconnecting system communication network; the integrated SBAS-GBAS system further comprising: an SBAS, comprising: an SBAS satellite that is configured to transmit SBAS correction and integrity data to a user; an SBAS receiver that is configured to receive navigation satellite data from the navigation satellite and convert it into SBAS augmentation data; an SBAS master station that is configured to receive the SBAS augmentation data from the receiver, to receive GBAS differential correction and integrity data from the interconnecting system communication network, and to transmit processed SBAS correction and integrity data that includes the received GBAS differential correction and integrity data to the SBAS satellite.
The invention also relates to an integrated SBAS-GBAS system comprising: a navigation satellite; an interconnecting system communication network; one or more GBASs, each GBAS comprising: a receiver that is configured to receive navigation satellite data from the navigation satellite over a navigation satellite to GBAS receiver communication path and convert the navigation satellite data into GBAS raw augmentation data; a processor that is configured to receive GBAS raw augmentation data over a receiver to processor communication path, the processor comprising: a network input connected to a GBAS to interconnecting system communication network communication path that is configured to receive formatted integrated system data from the communication network; a receiver input connected to a GBAS receiver to GBAS processor communications path that is configured to receive the raw augmentation data from the receiver; an augmentation data database; a Local Area Augmentation System (LAAS) message receiver that is configured to receive the formatted integrated system data from the network input, convert the integrated system data, and store it in the augmentation data database; a GBAS receiver augmentation data receiver that is configured to receive the raw augmentation data from the receiver input, convert the raw augmentation data, and store it in the augmentation data database; an integrity monitor checker that is configured to read data from the augmentation data database; a receiver status database that is configured to store receiver status data; an LAAS message formatter that is configured to accept information from at least one of the augmentation data database, the integrity monitor checker and the GBAS receiver status database, and is configured to create at least one of LAAS messages for output; a network output that is configured to accept LAAS messages from the LAAS message formatter and output them to the GBAS to interconnecting system communication network communication path; a transmitter/user output that is configured to accept LAAS messages from the LAAS message formatter and output them to at least one of a local transmitter and user; the integrated SBAS-GBAS system further comprising: an SBAS, comprising: an SBAS satellite that transmits SBAS correction and integrity data to a user over an SBAS satellite to SBAS user communication path; a receiver that is configured to receive navigation satellite data from the navigation satellite over a navigation satellite to SBAS receiver communication path and convert the navigation satellite data into SBAS augmentation data; a master station that is configured to receive the SBAS augmentation data from the receiver over an SBAS receiver to SBAS master station communication path, the master station further comprising: a network input connected to an SBAS to interconnecting system communication network communication path that is configured to receive formatted integrated system data from the communication network; a receiver input connected to an SBAS receiver to SBAS master station communications path that is configured to receive SBAS augmentation data from the receiver; an augmentation data database; an SBAS LAAS message receiver that is configured to receive the formatted integrated system data from the network input, convert the integrated system data, and store it in the augmentation data database; an SBAS receiver augmentation data receiver that is configured to receive the SBAS augmentation data from the receiver input, convert the SBAS augmentation data, and store it in the augmentation data database; an SBAS integrity processor that is configured to receive the SBAS augmentation data that is stored in the augmentation data database and configured to process integrity data; a correction processor that is configured to receive augmentation data from the augmentation database and the integrity data and produce SBAS correction and integrity data; an output that is configured to accept the SBAS correction and integrity data from the correction processor and output them to the SBAS satellite via the SBAS master station to SBAS satellite communication path.
The invention also relates to a method for operating a networked GBAS system, comprising: receiving navigation satellite data by a first GBAS; formatting navigation satellite data by the first GBAS into formatted GBAS differential correction and integrity data; transmitting the formatted GBAS differential correction and integrity data to an interconnecting system communication network; receiving the formatted GBAS differential correction and integrity data from the interconnecting system communication network by a second GBAS; formatting navigation satellite data by the second GBAS into further formatted GBAS differential correction and integrity data, utilizing the received formatted GBAS differential correction and integrity data from the first GBAS; transmitting the further formatted GBAS differential correction and integrity data to at least one of the interconnecting system communication network and a GBAS user.
The invention also relates to a method for transmitting SBAS correction and integrity data to an SBAS satellite, comprising: producing, by a GBAS processor, formatted integrated system data comprising GBAS raw augmentation data; receiving, by an SBAS master station, SBAS augmentation data from an SBAS receiver and the formatted integrated system correction and integrity data from a communication network; formatting, by the SBAS master station, SBAS correction and integrity data using the SBAS augmentation data and the GBAS differential correction and integrity data; and transmitting the SBAS correction and integrity data to an SBAS satellite by the SBAS master station.
Finally, the invention also relates to a method for operating an integrated SBAS-GBAS system that comprises a GBAS and an SBAS, the method comprising: receiving navigation satellite data by a GBAS receiver and an SBAS receiver; formatting GBAS raw augmentation data from the navigation satellite data by the GBAS receiver; transmitting, by the GBAS receiver, GBAS raw augmentation data to a GBAS processor; formatting GBAS raw augmentation data into formatted GBAS differential correction and integrity data by the GBAS processor; transmitting the formatted GBAS differential correction and integrity data to an interconnecting system communication network; formatting SBAS augmentation data from the navigation satellite data by the SBAS receiver; transmitting, by the SBAS receiver, SBAS augmentation data to an SBAS master station; receiving, by the SBAS master station, formatted GBAS differential correction and integrity data from the interconnecting system communication network; formatting, by the SBAS master station, SBAS correction and integrity data using the SBAS augmentation data and the GBAS differential correction and integrity data; and transmitting the SBAS correction and integrity data to an SBAS satellite by the SBAS master station.